Process and apparatus for cracking hydrocarbons



July 2, 1935. G. c. HARGROVE ET AL 2,006,571

PROCESS AND APPARATUS FOR CRACKING HYDROCARBONS Filed Feb. 20, 1928 2Sheets-Sheet l a A Nm am Hm uw @Mmm mmv .Sw ww uN @E Nw. NW

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NN NN July 2, 1935. Q Q HARGROVE ET AL 2,006,571

PROCESS AND APPARATUS FOR CRACKING HYDROCARBONS 2 Sheets-Sheet 2 FiledFeb. 20, 1928 is@ QM 5, om 'eofge @Hargrgten Wa//er E. Mon/gomery gn@l/tow? QN uw ww.

VPatented July 2, 1935 I UNITED STATES PROCESS AND APPARATUS FORCRACKING HYDROCARBONS Delaware Application February 20, 1928, Serial No.255,581

4 Claims.

This invention relates to improvements in apparatus for treatinghydrocarbon oils, and more particularly to apparatus for cracking crudeoil, reduced crude, fuel oil, petroleum residuums and other heavypetroleum oils.

In oil cracking systems in which the oil being treated is maintainedunder super-atmospheric pressure in the cracking zone, it is customaryto lead the conversion products to an evaporating chamber in which thepressure is reduced and the vaporization of the lighter fractions of theconversion products is facilitated. The evaporating chamber usuallyincludes, or has associated with it, means for separating the lighterfractions of the products of conversion from the heavier fractions.`Such means may, for example, comprise a dephlegmating column into whichthe hot vapors are introduced near the base and led upward incountercurrentrelation to relatively cool condensed portions of the vapors. Inorder to promote the condensation of the heavier fractions of saidvapors, it has also been proposed to introduce cold fresh stock into thecolumn directly into contact with said vapors. However, Where the freshstock has consisted of relatively heavy hydrocarbons such as crude oil,reduced crude or similar "dirty oils, there has been a tendency for theaccumulation of gummy or other diflicultly removable residues in thecolumn which tend to interfere with its effective working.

According to the present invention it is proposed to promote thecondensation of the heavier fractions of the conversion products in theseparating zone by bringing fresh stock from the stock line or othersource of supply into heat-exchanging relation with the conversionproducts, but maintained out of direct contact therewith while suchproducts are in a vaporous state. It is also proposed, when a freshstock consisting of unskimmed crude or the like is being used, to carrythe heat exchange to such a point that lighter fractions of such freshstock will be vaporizecl. These lighter fractions are then separatedfrom the unvaporized fractions and subjected to suitable refluxing orcondensing action to eiect a separation from the lighter gasolineconstituents of any heavier fractions carried with the gasoline vapors,which heavier fractions may either be introduced into the charging lineor stored or used in any suitable manner.

The invention also includes means forv mixing 'the condensed portion ofthe conversion products with the unvaporized portion of the fresh stockandfor controlling the proportions of each of these materials introducedinto the cracking zone.

The invention also includes means for maintaining the fresh crudeorother stock material under pressure in the preheating coils and meansfor bringing the thus preheated stock into a zone Where the pressure ismaintained. relatively low in order to facilitate the vaporization ofits lighter fractions.

One of the objects of the invention is to provide means for bettercontrolling the composition of the oil introduced into the crackingzone. Another object of the invention is to eiect more eiiicientutilization of the heat contained in the products of conversion comingfrom the cracking zone and the application of the heat thus extracted toVaporize the lighter fractions of the fresh stock, thereby eliminatingthe necessity for subjecting such stock to an initial distillation bymeans of heat from an extraneous source. Another object of the inventionis to promote condensation of the heavier fractions of the conversionproducts in the separating zone without introducing relatively heavy anddirty oil therein.

Other objects and advantages of the invention will appear from thefollowing description taken in conjunction with the accompanyingdrawings:

In the drawings:

Fig. l is a diagrammatic side elevation, partially in section, of anapparatus embodying one form of the present invention.

Fig. 2 is a diagrammatic side elevation of an apparatus in generalsimilar to that shown in Fig. l Withfthe furnace omitted and with thestructure modified to include a flash tower and an auxiliarydephlegmator.

Referring more particularly to Fig. 1 of the drawing, I indicatesgenerally the furnace which contains a plurality of heating coils Ilconnected by a transfer line I2 to a forged steel reaction chamber I4,in which the cracking continues and carbon is permitted to deposit. Thereaction chamber I4 is heavily insulated to prevent loss of heattherefrom, and is provided with manhole covers I5 at each end thereof,which may be taken olf during shutdowns to permit the removal of carbonfrom the chamber. The products of conversion other than carbon aredischarged from the conversion or reaction chamber I4 through thedischarge line I6 controlled by a pressure reducing valve Il. Thedischarge line I6 discharges into an evaporator I8, the overheadproducts from which pass through a line I9 into a imgTi-:Nr OFFICEdephlegmator or bubble tower 20 in which the vapors are reiiuxed. Thebottoms from the evaporator are drawn oi through a pipe 2I controlled bya valve 22, and pass first through a fuel oil cooler 23 and thence tostorage through the pipe 24. While not an essential element of thepresent invention, a level regulator 25, which may be of any well knowntype, is shown for controlling the liquid level in the evaporator I8.The regulator 25. controls the admission of steam to the steam line 26to open the power operated valve 22 when the level in the evaporatorrises too high, and shuts olf the supply of steam and permits the valve22 to close when the level drops below the desired position. In practicethere will be a nearl'lsteady drawoif of the fuel oil through the p1peThe overhead products from the dephlegmator 2Ilv pass through a vaporline 2'I to a condenser 28. Beyond the condenser 28 is arranged theusual valve controlled gasoline distillate receiver 29 having thecustomary valved outlet for permanent gases which controls the pressurein the condenser and fractionating apparatus. The reflux condensatecollecting in the bottom of the dephlegmator is drawn oi through theline 30 controlled by a power operated valve 3l and conducted to amixing or accumulator tank 32. The liquid level regulator 33, which issimilar to the regulator 25 on the evaporator I8, controls the admissionof steam to the steam line 34 and thereby controls the valve 3|. Thedischarge line I6 and the line 30 are shown as connected to an emergencycooler 35 by means of valved pipes 36 and 31 respectively, the valves inthese pipes being ordinarily closed, and opened only in the event thatit is necessary to withdraw the material under treatment from the systemunder unusual conditions.

The stock to be treated is picked up from a stock tank 38 by the lowpressure pump 39 and forced through line 40 to the pipe coils 4I and 42located in the tops of the bubble tower 20 and the evaporator I8,respectively. The coils 4I and 42 are provided with valve controlledby-passes 43 and 44, respectively. The heavy oil passing through thecoils 4I and 42 is preheated therein and serves to cool the vapors inthe two towers, the amount of stock passing through the coils beingregulated in accordance with the temperature conditions which it isdesired to maintain in the towers. It will be understood that automatictemperature controlled valves may be utilized if desired in connectionwith the coils 4I and 42 and their by-passes to correctly proportion theamount of oil passing through the coils. The outlet of coil 42 isconnected to a. line 45 which discharges into the mixing tank 32, apower operated valve 46 in this line being controlled by the levelregulator 41 -which governs the upper level in the mixing tank 32. vTheline is also connected to a pipe 48 controlled by a power operated valve49 and discharging into a return stock cooler 50. The level regulator 41controls both the valve 46 and the valve 49, the connections being suchthat one valve is opened as the other is closed. The amount of freshstock necessary to maintain the proper temperature in the bubble tower20 and the evaporator I8 is usually more than sufficient to maintain theproper level in the mixing tank 32, and therefore the excess oil isby-passed through the pipe 48 into the return stock cooler 5U and fromthere returned through the line 5I to the stock'tank 38. By means ofthis arrangement the relative amounts of fresh feed and refluxcondensate from the bubble tower fed into the mixing tank to make up thecharging stock'may be controlled, at the same time permitting theregulation of the temperatures of the evaporator and the bubble tower bycirculating the necessary amount vof fresh stock through the coils 4Iand 42 as a cooling medium independently of the make-up require.- ments,since the excess `stock is returned to the stock tank.

Where the mixing tank is operated under pressure, the control valve 46may be replaced by a check valve preventing back flow from the mixingtank. In this case, when the level regulator 41 opens the valve 49 inthe line 48 leading to the return stock cooler, the fact that thepressure in the cooler is less than that in the mixing tank will causethe excess oil to flow through the cooler.

An annular `pan 52 is placed beneath the coil 42 to collect thehydrocarbons condensed in the upper part of the evaporator I8, and a runback 53 conducts this condensate to the bubble tower 20.

A line 54 is connected to the bottom of the mixing tank 32 and to thesuction side of a booster pump 55. The outlet from the booster pump 55connects tothe suction side of a high pressure hot oil pump 56, thedischarge side of which, in turn is connected by a line 5l to the inletof the heating coils II. A vent line 58 is connected to the top of themixing tank 32 and discharges into the bubble tower 20 above the liquidlevel therein, for example, between the fifth and sixth plates, topermit vapors which may be generated in the tank 32 to be fractionatedin the bubble tower 20.

The discharge side of the low pressure pump 39 is also connected to thetank 32 by a pipe 59 controlled by a power operated valve 60 governed bya regulator 6 I The regulator 6I establishes a minimum level for themixing tank 32, and in the event of the level dropping down asfar as therange of the regulator 6I, the valve 60 is opened and stock passeddirectly into the mixing tank 32 to obtain the necessary minimum leveltherein. In practice this situation will never arise and this is merelya safeguard to prevent the suction line 54 connected to the chargingpumps 55 and 56 from becoming uncovered. It is very undesirable topermit the cold stock to enter the tank 32 for the reason that thiswould throw oil' the temperature balance existing throughout the system,and it is therefore desirable for the operator to watch either the oatarm on the regulator 6I or the liquid level in an ordinary gauge glassadjacent thereto, so that the pump 39 may be speeded up, or the chargingpumps and 56 slowed down to permit the level in the mixing tank to buildup rather than to maintain this level by the addition of fresh, coldstock directly to the tank.

When the apparatus is being operated on crude oil, the crude iswithdrawn from the tank 38 by the pump 39, preheated in the coils 4I and42 and discharged into the tank 32, where it is stripped of its naturalgasoline content and the skimmed crude mixed with the clean overheadrecycle stock, discharging from the bottom of the bubble tower 20. Thismixture is drawn olf through the line 54 by the pumps 55 and 56 andcharged into the heating coils II of the furnace I0 where it is raisedto a cracking temperature. From there the material being treated isdischarged into the reaction chamber I4, and is then vaporized by itscontained heat under reduced pressure in the evaporator I8, the heavyresidual oil being drawn oif from the evaporator I8 through the line 2|and sent to storage. The residual material drawn off from the evaporatorI8 is marketable fuel oil, and is relatively free from bottom settlingsas compared with the fuel oil bottoms produced by the cracking of asimilar stock in a pressure distillation process. The vapors from theevaporator I8 pass into the bubble tower 20 through the line I9, thecondensate collecting in the bubble tower being directed to the mixingtank 32 as described, and the gasoline distillate from the dephlegmatorbeing condensed under pressure if desired in the condenser 28. Thenatural gasoline contained in the preheated crude will be largelystripped therefrom in the mixing tank 32 and will pass into the bubbletower 20 through the line 58, being mixed with the cracked gasoline inthe 'final gasoline distillate. To promote easy stripping of the crude,it is desirable to introduce the preheated crude into the mixing tanknear the top thereof and above the inlet for the recycle stock, as shownin the drawing. Although the bubble tower 20 and the mixing tank 32' areunder substantially the same pressure by reason of being in free andopen communication through the vent line 58, the positive discharge ofrecycle stock from the bubble tower to the mixing tank is assured bymounting the mixing tank at a lower level, thus giving a hydrostatichead.

If desired, as for example when a crude oil having a relatively highgasoline content is being treated, the line 45 may be connected with asupplementary evaporator or flash tower 62 as shown in Fig. 2. In thiscase a pressure regulating valve 63 may be provided in the line 45, sothat the crude in the coils 4I and 42 may be maintained under asubstantially higher pressure than is maintained in the iiash tower 62in order to secure the maximum stripping action. The flash tower 62 isshown as connected by aline I9a with a separate fractionating system,such as the dephlegmator or bubble tower B4, thus permitting the naturalgasoline from the crude to be collected separately from the crackedgasoline. The condensate collecting in the dephlegmator 64, which willconsist substantiallyof kerosene and fractions of similar gravity, maybe led to the mixing tank 32 through the line 65 or to storage through aline 56, by suitably manipulating the valves 6l and 68. The strippedcrude which collects in the bottom of the flash tower 62 may be ledcontinuously or intermittently to the mixing tank 32 through the line 69controlled by valve 10. The emergency cooler 35 and the return stockcooler 50 are omittedfrom the showing in Fig. 2. However, it will be`understood that either or both of these features may be included.

If desired, the flash tower 62 may be omitted, in which event the line45 will lead directly t0 the mixing tank 32 and a line leading to thesupplemental dephlegmator 64 instead of to the dephlegmator 20 may beprovided, thus insuring the collection of the natural gasoline and thecracked gasoline separately. In this case the mixing tank may beadvantageously operated at a lower pressure than that existing in thedephlegmator 20, for example, at atmospheric pressure, in order tosecure the maximum stripping action.

Another possible modification of the apparatus is to eliminate themixing tank and use the bottom of the dephlegmator 20 as a reservoir toperform the functions of the tank 32. In such case,

the line 54 connected to the suction side of the chargingpumps 55 and 56would be connected directly to the bottom of the dephlegmator 2l), andthe preheated crude line 45 would discharge into the dephlegmator 20 ator about the same level as the vapor inlet line I9 from the evaporatorI8. The pipe 48 and the power-operated valves 45 and 49 would be used asshown, but would be controlled simultaneously by a level regulator onthe dephlegmator 20 similar in construction to the regulator 41.However, we prefer to employ the mixing tank 32 because of theflexibility of control thereby provided, particularly with respect tothe disposition of the natural gasoline stripped from the crude,operating the mixing tank at a different pressure than that existing Linthe dephlegmator, and maintenance of the desired ratio of fresh stock torecycle stock Vin the charging, mixture, all as above described.

An additional operating advantage of the mixing tank is that it iseasier to clean the tank of any fouling which may occur from using adirty residual oil as the fresh feed than it would be to clean thedephlegmatorif a similar charging stock were discharged directlythereinto.

Other changes and modifications will suggest themselves to those skilledin the art, and we therefore do not desire to be limited except by thescope of the appended claims.

What we claim is:

1. In an oil cracking system, a cracking unit including a reactionchamber, an evaporator connected directly with the reaction chamber andto which products of conversion are transferred from the reactionchamber, a dephlegmator, means for passing vapors from the evaporatordirectly to the dephlegmator, a coil in said evaporator in the path ofvapors passing therefrom, a coil in the dephlegmator in the path ofvapors passing therefrom, a mixing tank, means for passing a chargingstock serially through said coils and into the mixing tank, means forpassing reflux condensate separated in the dephlegmator to said mixingtank, and means for transferring the mixture collected in the mixingtank to the cracking unit.

2. In an oil cracking system, a cracking unit including a reactionchamber, an evaporator connected directly with the reaction chamber andto which products of conversion are transferred from the reactionchamber, a dephlegmator, means for passing vapors from the evaporatordirectly to the dephlegmator, a coil in said evaporator in the path ofvapors passing therefrom, a coil in the dephlegmator in the path ofvapors passing therefrom, a mixing tank, meansfor passing a chargingstock serially through said coils and into the mixing tank, means forpassing reflux condensate separated in the dephlegmator to said mixingtank, means for passing vapors separated in the mixing chamber to saiddephlegmator, and means for transferring the mixture collected in themixing tank to the cracking unit.

3. An oil cracking apparatus comprising in combination a heating coil, avapor separating chamber dephlegmator and a final condenser seriallyconnected in the order named; a crude oil stripping tank; a coil withinsaid dephlegmator and another coil within the vapor space of saidchamber; means for withdrawing oil from said chamber; means for passingcrudeoil serially through the coils within said dephlegmator and chamberand thence into said stripping tank; means for passing reiiux condensatefrom said dephlegmator into said tank, and means for supplying liquidunder'pressure from said tank to said heating coil, and a vaporconnection between said tank and dephlegmator.

4. The process of treating hydrocarbon oil which comprises passing oilthrough a cracking zone wherein it is raised to a cracking temperatureand subjected to conversion, introducing the resulting cracked productsinto a separating zone wherein vapors separate from liquid residue,-withdrawing said liquid residue from said separating zone, passingvapors from said separating zone into a fractionating zone whereinfractional condensation thereof occurs, removing fractionated vaporsfrom said fractionating zone and condensing them as a desired product,removing reiiux condensate from said fractionating zone and introducingit into an accumulating zone, passing fresh charging Vstock in indirectheat exchange relation with vapors resulting from the separatingoperation taking place in said separating zone, introducing theresulting preheated fresh charging stock into said accumulating zone,removing light fractions from said accumulating zone, as vapors,condensing a portion of the rst mentioned vapors in said separating zoneand collecting the resulting condensate free from portions of saidliquid residue, passing condensate so collected into said fractionatingzone, and removing liquid oil from said accumulating zone and passing itto said cracking zone for conversion therein.

GEORGE C. HARGROVE. WALTER B. MONTGOMERY.

